Two proteins, the hormone-binding protein neurophysin, and the iron-sequestering protein ferritin will be investigated. Neurophysin contains internally duplicated segments, but under most conditions, only a single hormone- or peptide-binding site is seen. In order to understand the significance of the internal duplication, the relationship between the principal binding site and the duplicated and non-duplicated segments will be studied by affinity-labeling and by nuclear magnetic resonance spectroscopy; chemical and enzymatic modification will also be used to assess the role played by individual residues in binding or in the maintenance of conformation. Additionally, thermodynamic studies aimed at resolving the contribution of the amino-carboxylate salt-bridge to the overall stability of neurophysin-hormone complexes and at interpreting the negative enthalpy of neurophysin-hormone interaction are planned. Ferritin studies are particularly aimed at evaluating the magnitude and significance of potential interactions between the iron-containing core and the protein shell and at determining the extent to which the inorganic phosphate of the core plays a role in either interactions with the protein shell or in the iron-incorporation process.